Roof deck systems, composed of a high tensile steel base with thermal insulation and high performance mineral board mechanically anchored to the steel sections, provide composite strength. The resultant assembly is a strong, durable substrate for roofing applications. Composite roof deck assemblies are disclosed in U.S. Pat. No. 4,601,151; U.S. Pat. No. 4,736,561; U.S. Pat. No. 4,707,961; U.S. Pat. No. 4,783,942 and U.S. Pat. No.: 5,584,153.
Corrugated steel sections are positioned over structural supports and anchored in place with welded connections through special weld washers, of the type disclosed in U.S. Pat. No. 4,601,151, or with mechanical fasteners. Thermal insulation, available in a variety of types and thicknesses, is placed over the steel sections. High density tongue-and-grooved mineral board panels are placed over the thermal insulation or directly on the steel sections.
Corrosion resistant screw fasteners anchor the thermal insulation and mineral board to the steel sections, thereby developing composite strength and stability for the roofing foundation. Corrosion resistant compression discs provide concentrated load deflection continuity at all abutting mineral board locations. Pressure sensitive weather resistant tape is applied over all mineral board joints to provide a continuous plane across the joints of the roof covering foundation. With the application of joint tape, the roof deck assembly is complete and ready to receive the roof covering.
U.S. Pat. No. 4,601,151 discloses a roof system comprising a sheet of corrugated material having ridges and a rigid substrate, such as a mineral board, fastened to the upper ridges of the corrugated sheet. The corrugated sheet is welded to roof purlins. The mineral board, on the other hand, is fastened to the corrugations of the corrugated sheet by threaded fasteners which extend through the mineral board and through the ridges to form a truss-like structure that spans between the roof purlins.
When an insulated roof is desired, insulation is interposed between the mineral board and the corrugated sheet. As the insulation thickness increases the length of the threaded fasteners increases, creating potential rotation and bending problems for the fasteners. As a result, the thickness of the insulation is limited by the threaded fastener length. Additionally, since fasteners typically extend all the way through the roofing layers from the exterior of the roof to the interior supporting structure of the roof, thermal shorts may be created between the exterior of the roof and the interior of the roof, which is undesirable in extremely hot or cold climates.
Although the roof may be well insulated, the temperature of the metallic sheets changes significantly during a 24 hour period when the temperature gradient between the interior and exterior of the building is high. For example, the temperature of a steel deck on an air-conditioned building will gradually increase and decrease. Thermal expansion and contraction of the steel sheets and the steel purlins can cause movement of adjacent surfaces, which generates noise when the surfaces rub or work against each other. Expansion and contraction creates noise at the juncture between edges and ends of the sheets and between the lower surface of the sheets and upper surfaces of the purlins which support them.
Architectural designs may feature roofs which are flat or inclined without an insulated ceiling between the roof and the interior of the building. Generally, an insulated ceiling will serve as an acoustical barrier so that popping and cracking noises resulting from thermal expansion of the steel roof deck is not a problem. However, when the insulated ceiling is eliminated, unwanted noise may become a problem. For example, in the sanctuary of a church, constructed without a ceiling, in a hot sunny climate, thermal expansion of steel sheets in the roof deck may result in excessive noise during church services. The noise is particularly noticeable during prayer or other periods of silence.
Recently, exposed steel composite roof decks have been utilized more and more on specialized applications where no ceiling is utilized and the roof deck is exposed on the interior of the structure. While this type of construction is not new, designers have found themselves more and more on projects where the interior use of the structure requires a high degree of "quietness." When exposed steel composite roof decks are used on church sanctuaries, where during prayer and meditation times, the occupants expect quiet to reign within the building. Other buildings such a libraries, media centers, condominiums and classroom teaching areas are also using this type of design.
It has been reported that under certain conditions and at particular times of the year, ministers had trouble conducting services because of the popping and crackling noises emanating from the roof deck. The noises, popping sounds, occurred every two to three seconds and were very distracting. The noise level reached its peak at high noon, or during maximum thermal exposure, which is often the time for church services.
Investigation revealed that while the noises were not exactly the same in all cases, the degree of disturbance was real in all cases and a solution to the noise problem was required if this type of architectural design were to be implemented successfully.
The noise can be generated by three separate conditions.
Condition 1: Interior of the Building
Movement of the steel deck section within the assembly produced popping noises. This movement can be caused by walking over the deck surface or, as more commonly seems to occur, by thermal changes of the steel section due to heat loading from the sun. It has been observed that, even in highly insulated roof deck assemblies (R=30 type of insulation), the temperature of the steel deck can cycle up to 40 or 50 degrees F. during a normal day. This change in temperature produced movement of the steel deck section. Additionally, friction between the top of the steel section and components, such as thermal insulation or mineral board, laid directly on top of the steel also produce noise.
Condition 2: Perimeter of Building
The same situation exists where the building has steel supporting members exposed to the outside temperatures, such as at overhangs. The supporting steel moves under thermal changes and causes movement of the steel decking, which causes noises or popping. The popping noise is generated at the contact points between the steel deck and the steel supporting structure.
Condition 3: Metal Roofing
It was observed that most metal roofs make noises when expanding and contracting under thermal change.
A need exists for a method and apparatus for preventing unwanted noise as a result of thermal expansion or other variable loading of structural members and particularly between structural members used in roof decks.